A known technology arranges storage devices in a storage apparatus into a hierarchy according to response performance for accesses and relocates data between levels in the hierarchy. As one example, data that is accessed frequently is placed in high-performance storage devices and data that is accessed infrequently is placed in low-performance storage devices. By arranging data in this way, high-speed access is possible.
One proposed technology for arranging storage devices into a hierarchy is described below. As one example, storage regions that form the volumes of a main and a standby storage system are arranged into respective hierarchies. During a failover, the volume of the standby storage system is migrated to levels in the standby storage system that correspond to the levels of the volume of the main storage system.
In another proposed technology, a primary page and a secondary page with the same data content are stored on a solid state drive (SSD) and the secondary page is moved to a serial ATA (SATA) disk that has a lower cost than the SSD when a pair suspend command has been received.
With yet another proposed technology, when data is copied remotely, a storage apparatus at the copy destination copies data into a storage device that is provided within the storage apparatus and corresponds to the storage level at the copy source.
See, for example, the following documents:
Japanese Laid-Open Patent Publication No. 2007-328468;
International Publication Pamphlet No. WO2011-111093; and
Japanese Laid-Open Patent Publication No. 2007-265403.
In some storage systems with redundant storage apparatuses, data stored in the storage apparatus currently in use (i.e., active) is backed up in a storage apparatus currently on standby. In addition to such backup function, it would also be conceivably possible to arrange the storage devices in the respective storage apparatuses into hierarchies and to relocate data between the levels in the hierarchies. In such a situation, data is relocated in the active storage apparatus in accordance with how frequently the data is accessed from a host apparatus. On the other hand, at the standby storage apparatus, since accesses from a host apparatus are not received, data transmitted from the active storage apparatus for backup purposes ends up being placed on any level in the hierarchy regardless of how frequently the data is accessed from the host apparatus. If a failover occurs in this state, there is a problem that the improvement in access speed produced by arranging the storage regions into a hierarchy is no longer obtained when a storage apparatus that has switched from the standby state to the active state receives accesses from a host apparatus.